Measurement of a fiber direction of a carbon fiber material and fabrication of an object in carbon fiber composite technique

ABSTRACT

The fiber direction of a carbon fiber material of a test object is detected by means of the polarization direction of light reflected by the test object. If, for example, non-polarized light impinges upon carbon fibers, light reflected by the fibers is polarized in fiber direction.

BACKGROUND OF THE INVENTION

The present invention relates to a concept for measuring a fiberdirection of a carbon fiber material, like for example for qualitytesting and/or further processing and for a manufacturing of an objectin a carbon fiber composite construction.

In modern lightweight construction, more and more carbon fibers are usedfor increasing the strength of so-called carbon fiber compositematerials. In particular with safety-critical members made of thesecomposite materials, like e.g. in aircraft construction, automobileconstruction or the like the correct position and the correct course,i.e. the direction of the carbon fibers are of decisive importance forthe mechanical strength and load capacity of the complete member. At anypoint or at any relevant points of the work piece, it is a need tomeasure the fiber course or the angle in which the carbon fibers arepositioned with a certain accuracy. Conventionally, in manufacturingseveral layers of carbon fiber fabrics are stacked, one after the otheron top of each other and each soaked with special plastics and hardenedor cured. Each of these layers has to be qualified with respect to thefiber course. As the carbon fiber layers are non-transparent for visiblelight, testing the fiber direction has to be executed individually foreach layer each after depositing the layer.

Until now, the fiber direction has been measured or controlled indifferent ways, i.e. a) visually by the production staff, b) bydepositing marks by the production staff, detecting the marks by meansof a camera system and further processing the camera images by acorresponding software, and c) by recording the carbon fibers using acamera system whose pixel resolution has to be so high, however, thatthe individual carbon fibers are visually resolved so that from theimage data by means of a special software the direction of the carbonfibers may be determined in any place of the image.

Solutions a) and b) need the help of the production staff and are thusdifficult to reproduce and error prone due to the known subjectiveeffects. Apart from that, the solutions are time-consuming and thusexpensive. A completely automated testing is not possible. Solution c)needs a comparatively high pixel resolution of the used camera. Apartfrom higher costs for a camera with a high resolution, with higher pixelnumbers more image data result, which leads to a higher imagetransmission speed and a higher computing power for image evaluation atthe same bitrate. A higher data rate and high computing power again leadto higher costs. On the other hand, this means that with a certainexpenditure the testing speed is limited. Finally, this means that fortesting a certain area of a carbon fiber composite member, acceptablecosts determine the testing speed. A further disadvantage is the factthat the fiber direction has to be calculated by software from the imagedata. The accuracy and reliability of the results thus substantiallydepend on the quality of the software. In particular with fabric soakedby plastics, the detection of the fiber direction is substantially moreinaccurate and less reliable than with a non-soaked so-called “textile”fabric.

Thus, a concept for measuring the fiber direction of a carbon fibermaterial would be desired or a concept for manufacturing an object in acarbon fiber composite construction which overcomes above mentioneddisadvantages or enables a more cost-effective manufacturing with thesame quality or accuracy.

SUMMARY

According to one embodiment, a device for measuring a fiber direction ofa carbon fiber material of an object to be tested or device under testmay comprise the following feature: a polarization sensor for detectinga polarization direction of light reflected by the object to be tested,wherein the polarization direction indicates the fiber direction.

According to a further embodiment, a system for manufacturing an objectin carbon fiber composite construction may comprise the followingfeatures: a device for measuring a fiber direction of a carbon fibersheet of a carbon fiber material of a test object having a polarizationsensor for detecting a polarization direction of light reflected by theobject to be tested, wherein the polarization direction indicates thefiber direction; and a manipulator for stacking the carbon fiber layerson top of each other by adjusting the fiber directions of the carbonfiber layers according to the measurement by the device.

According to a further embodiment, a method for measuring a fiberdirection of a carbon fiber material of a test object may comprise thefollowing steps: illuminating the test object or object to be tested;and detecting a polarization direction of light reflected by the testobject, the polarization direction indicating the fiber direction.

A further embodiment may comprise a computer program having a programcode for executing the inventive method for measuring a fiber directionof a carbon fiber material of a test object when the program is executedon a computer.

The present invention utilizes the finding that it is possible to detectthe fiber direction of a carbon fiber material of a test object usingthe polarization direction of light reflected by the test object. If,for example, non-polarized light impinges upon carbon fibers, lightreflected by the fibers is polarized in fiber direction. The wavelengthof the light is for example in a range of 400 to 1000 nanometers.

It is possible to visually measure the fiber direction of the carbonfiber material, like e.g. a carbon fiber fabric or a carbon fibercomposite material by means of the polarization of light. According toone embodiment, as a polarization sensor accordingly apolarization-sensitive camera is used which records the test object toacquire a spatially resolved detection of the polarization direction andthus a spatially resolved sampling of the fiber direction.Advantageously, it is not necessary for the resolution of thepolarization-sensitive camera to suffice to optically resolve thefibers. In other words, the spatial resolution of thepolarization-sensitive camera in the object plane of the lens orobjective of the camera may be less than it would be needed to resolvethe structure of the fibers on the surface of the carbon fiber material,i.e. the pixel repeat distance in the object plane of the lens may begreater than for example the fiber radius.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, embodiments of the present invention are explained inmore detail with reference to the accompanying drawings, in which:

FIG. 1 is a schematical block diagram of a device for measuring a fiberdirection of a carbon fiber material of a test object according to anembodiment of the present invention;

FIG. 2 is a schematical illustration of a polarization-sensitive camerafunctioning as a polarization sensor according to one embodiment; and

FIG. 3 is a block diagram of a system for manufacturing an object in acarbon fiber composite construction according to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a device for measuring a fiber direction of a carbon fibermaterial of a test object according to one embodiment of the presentinvention. The carbon fiber material may, for example, be a carbon fiberfabric as it is illustrated in FIG. 1 by the cross hatching. It may,however, also be a carbon fiber composite material. In FIG. 1, the testobject 10 of the carbon fiber material is for example a sheet or alaminate of carbon fiber fabric which is, for example, provided to beapplied after measuring to one or several other carbon fiber sheets inorder to then also result in a carbon fiber composite. In this respectit is important to know the fiber directions of the carbon fibermaterial. The fiber direction may, however, also be needed for otherreasons. In FIG. 1, in the dashed enlargement 12, as an example a viewonto a front side 14 of the test object 10 and its carbon fiber materialis illustrated. Therein, fiber bundles 16 are interwoven into a fabric18. Alternatively, the object may be a stack of above-mentioned carbonfiber sheets—with or without plastics matrix, which may be cured orstill uncured, i.e. it may be a product or intermediate product of acarbon fiber composite material.

The device for measuring the fiber direction of the carbon fibermaterial 18 of the test object 10 of FIG. 1 is generally designated by20 and includes a light source 22, a polarization sensor 24 andoptionally a computer 26 and optionally further a monitor 28. The lightsource 22 is implemented to illuminate the test object 10. Thepolarization sensor 24 is implemented to detect a polarization directionof light reflected by the test object 10, i.e. in particular light usingwhich the test object was illuminated by the light source 22 and whichis then reflected into the polarization sensor 24, wherein thepolarization direction indicates the fiber direction of the object 10 atits illuminated front side 14.

In the assembled state, the light source 22 is thus aligned toilluminate the test object 10. The light 30 emitted by the light source22 is for example non-polarized. It is for example a halogen lamp,thermionic lamp, LED or the like. Simultaneously, several lamps of thesame or a different type may illuminate the object 10 from differentdirections or with the help of other devices like mirrors, opticalfibers or the like an illumination from several directions may berealized, i.e. the light source may comprise several lamps and/oradditional light guiding means, like e.g. mirrors, etc. in order torealize an illumination of the object 10 from different directions andto thus acquire a more complete illumination of the surface 14 sampledby the polarization sensor 24 or facing the same, i.e. preventingshadowings, etc. The light spectrum of the light 30, like e.g. itsaverage wavelength, is for example in a range from 400 to 1000 nm. Inparticular, the light source 22 may be a wide band or narrowband lightsource. It is also possible to use a monochromatic light source 22.Advantageously, a half-width of the spectrum of the light source 22 isin a range smaller than or equal to 100 nm.

As soon as the light 30 impinges upon the test object 10, theadvantageous characteristic of the carbon fiber material 18 has apositive effect, according to which the latter is polarizing for lightimpinging upon the same. In particular, light 30 is polarized after itsreflection at the carbon fiber material of the test object 10 along apolarization direction which passes along the fiber direction at theilluminated surface 14. In the enlarged section 12, which shows a topview onto a section of the surface 14 of the object 10 from thedirection of the polarization sensor 24, this is exemplarily illustratedfor two different positions A and B of the test object. The light 32reflected at position A and impinging upon the polarization sensor 24comprises a polarization direction 34 _(A) which passes in parallel tothe fiber direction 36 _(A) of the fiber bundle 16 which crossesposition A. At position B, the fiber direction 36 _(B) and thus also thepolarization direction 34 _(B) which passes in parallel to the same runsin a different direction, i.e. perpendicular to the direction 36 _(A) or34 _(A), as position B is exemplarily located at a different fiberbundle 16.

The polarization sensor 24 may be one which only measures the fiberdirection of the carbon fiber material 10 point-wise across thepolarization direction of light 32 reflected at this point or may be aline or area sensor or a polarization-sensitive camera. In the firstcase mentioned, if it is desired, for a spatially resolved sampling ofthe fiber direction for example a manipulator or a robot (notillustrated) may be used to laterally shift or vary the point orlocation sampled by the polarization sensor 24 from which reflectedlight is detected by the polarization sensor 24 and to thus acquirecorresponding fiber direction measurements at different positions A andB.

FIG. 2 shows that the polarization sensor 24 may be apolarization-sensitive camera. According to this embodiment, thepolarization-sensitive camera 24 includes a pixel array 38 and anobjective 40 for imaging the test object 10 onto the pixel array 38. Asillustrated in the enlarged top view 42 onto the pixel array 38 in FIG.2, the pixels 44 of the pixel array 38 may for example be grouped intosuper-pixels 46, so that the super-pixels 46 each comprise pixels 44 ofthe pixel array 38 which are sensitive with respect to differentlypolarized light, i.e. at least a first pixel for a first polarizationdirection and a second pixel for a second different polarizationdirection. FIG. 2 exemplarily illustrates that each super-pixel 46 forexample comprises four pixels 44 which are sensitive with respect topolarization directions spaced apart from each other by 40° angledifferences. Another number of pixels with a different polarizationsensitivity is of course also possible, just like a non-equiangulardistribution of the polarization directions of those pixels. It is to benoted that it is not important whether, as illustrated in FIG. 2, thepixels are arranged regularly in lines and columns, in a differentregular arrangement or irregularly, or whether the arrangement of thepixels within the super-pixels 46 is the same or whether the arrangementof the pixel sensitive to the different polarization directions withinthe super-pixels 46 varies across the pixel array 38. It is likewisepossible for the super-pixels 46 not to be arranged regularly in lineand column direction but the same may also be arranged differently in aregular or irregular way.

Sampling by the polarization sensor 24 is not limited to a point or areasampling, as described above. It would also be possible to execute asampling in lines or a one-dimensional sampling of the fiber directionof the carbon fiber material of the test object 10 at the illuminatedfront side 14. Also here, a relative movement between object 10 andpolarization sensor 24 may be used to all in all acquire atwo-dimensional sampling of the fiber direction.

The polarization sensor 24 may further comprise a filter system tofilter out light of a certain wavelength from the reflected light 32,like e.g. the light of a wavelength in the above mentioned range between400 to 1000 nm. The pixel array 38 may, for example, comprise an arrayof light-sensitive areas above which again an array of filter structuresis located, so that each light-sensitive area together with a filterstructure results in a pixel. The filter structures upstream from theindividual light-sensitive areas may, for example, be grid structures.It would in particular be possible for the filter structures to comprisestructure elements having dimensions within the sub-wavelength range,i.e. smaller than the wavelength of light 30. The filter structures maycomprise characteristics of a photonic crystal. Light-sensitive areasand filter structures may together be integrated in a chip. Thelight-sensitive areas may, for example, be formed by a photodiode array,a CCD array or a CMOS pixel array. Such a polarization sensor is forexample described in DE 102008014334.

The polarization sensor 24 may also consist of a conventional CCD orCMOS image sensor, i.e. a sensor which is not sensitive to polarization,i.e. a single, line or image sensor, and a device arranged between thesensor and the object 10 for a continuous or gradual rotation of thepolarization direction of light 32, i.e. a polarization filter whosepass-through polarization direction is temporally varying. The devicefor rotating the polarization direction of light or the polarizationfilter with a varying pass-through polarization direction enables, oneafter the other, i.e. sequentially in time, to record several images andto combine the same in a suitable way in order to this way acquire thelocal polarization angle at each location of the surface 14.

As it was illustrated in FIG. 1, the device 20 may optionally comprise acomputer 26 and a display device 28. The computer 26 may for example beprovided to convert the pixel values of the super-pixels in a case of animplementation of the polarization sensor 24 as an area sensor intosuitable scalar values, i.e. one or several per super-pixel, which areamong others a measure for the local polarization angle of the reflectedlight 32 at the location of the surface 14 associated with thesuper-pixel or for the fiber direction at this location. On the displaydevice, the spatially resolved sampling of the fiber direction may bedisplayed in a color-encoded way. The computer 26 or a program executedtherein may further control the above-mentioned optionally existingmanipulator 48 for generating a relative movement between object 10 andpolarization sensor 24.

The computer 26 may in particular also act as a controller whichdetermines the orientation of the fiber direction of the object 10 withrespect to the shape or design of the object 10 from the fiber directionof the carbon fiber material of the object 10 determined via thepolarization sensor 24 and position information regarding the object 10and controls a manipulator depending on this orientation which holds theobject, in other words, the controller may control a manipulator forholding and changing the position of the object depending on theposition information on a position of the object 10 relative to thepolarization sensor 24 and the fiber direction of the object, to controla manipulator for adjoining the object and another object so that in anadjoined or contacting state the fiber direction comprises apredetermined orientation relative to the other and/or depending on theposition information regarding a position of the object 10 relative tothe polarization sensor 24 and the fiber direction of the object, todetermine an orientation of the fiber direction with respect to a designof the object 10. Contacting or adjoining may be executed so that theside 14 in a contacting state adjoins the other object, i.e. for exampleso that the fiber direction has a predetermined directional relation toa designated preferential direction of the corresponding facing side ofthe other object, like e.g. a carbon fiber direction, like e.g.transverse to the same. Of course the above mentioned manipulator mayalso be the one which holds the object at the position defined by theposition information at the moment of detecting the polarizationdirection and thus the fiber direction. In the following, an example inthis respect is described within the scope of a manufacturing system.

FIG. 3 shows a system for manufacturing an object 50 in a carbon fibercomposite construction according to one embodiment. The system generallydesignated by 52 uses or includes the device 20 of FIG. 1 and amanipulator or robot 54. As described, the device 20 executes themeasurement of a fiber direction of carbon fiber layers 56. The robot 54is implemented to spread the carbon fiber layers 56 adjusting the carbonfiber directions of the same with respect to each other according to themeasurements by the device 20 in order to this way acquire the object50. For example, a controller may be provided which controls the robot54 and evaluates carbon fiber directions determined via the polarizationdirection of the reflected light.

The controller 58 would for example control the manipulator or robot 50so that the device 20 may determine the fiber direction of the carbonfiber layer 56, i.e. that the object 10 is illuminated and in the focusof the polarization sensor 24. Knowing the position of the objectrelative to the polarization sensor when detecting the polarizationdirection and the detected polarization direction, the controller 58would then get to know an orientation of the fiber direction relative toa shape or design of the object 10 and may for example control the robot54 so that the current carbon fiber layer 56 is applied onto alreadysuper-positioned other carbon fiber layers 60 so that the fiberdirection of the carbon fiber layer 56 to be currently applied forms apredetermined angle with the fiber direction of the currently exposedcarbon fiber layer, which for example leads to an especially stableshape of the object 50. The object 50 may be, for example, as indicatedin FIG. 3, the hull of a ship or a part of a body of an airplane or partof a motor vehicle.

A means 60 indicated in FIG. 3 by the dashed boxes 60 and, ifapplicable, also controlled by the controller 58 may be provided toprovide the carbon fiber layers with plastics so that the carbon fiberlayers are embedded in plastics, the so-called matrix, after a hardeningor curing of the plastics. Providing the carbon fiber layers withplastics may be executed individually before respectively depositing therespective layer, individually each after depositing the respectivecarbon fiber layer or for several carbon fiber layers together in onestep after stacking the same on top of each other.

An advantage of the above embodiments is the direct receipt ofinformation via the fiber direction without being dependent on patternrecognition or the like. The measured polarization direction directlyresults in the fiber direction at the respective position of the testobject and measurement may thus be executed quickly and reliably and inparticular does not delay manufacturing in case of FIG. 3.

In other words, above embodiments are based on the fact that carbonfibers have the characteristic to partially reflect incoming light whichis generally not polarized and to polarize here in parallel to thelongitudinal fiber direction. This characteristic of polarizing behavioris utilized in the above embodiments to determine the fiber direction.In this respect, a visual measurement of polarization is used. By meansof a device which is suitable for such a visual measurement, lightreflected by the carbon fibers, like, e.g. a carbon fiber fabric, isanalyzed with respect to the direction of the polarization direction.The result then directly represents the direction of the carbon fibersat the respective position. The device may be suitable for a visual,two-dimensional detection and analysis of the polarized light, as it wasdescribed with respect to FIG. 2, which shows a polarization-sensitivecamera or a “polarization camera”. According to some embodiments, thetest object of carbon fibers is illuminated by a suitable light source,wherein a polarization camera is directed to the object. Thepolarization direction of the reflective light measured at everyposition of the object by the camera directly indicates the direction ofthe carbon fiber at this position. The wavelength of the light may, forexample, be in a range from 400 to 1000 nm. As it was already indicatedabove, it is advantageously not necessary for the resolution of thecamera to be so high that the fibers have to be detected individually inorder to be able to calculate the direction of the fibers by software.To the contrary, the fibers themselves polarize the light inlongitudinal fiber direction and the camera only has to be able toanalyze the polarization in a spatially resolved way. This means that incase of FIG. 2 the pixel resolution of the camera may be clearly lowerthan in case of the method according to c) mentioned in the introductorypart of the description of the present application. Due to the low datarate and low computational effort this leads to low system costs. Or inother words, in case of the above embodiments a larger area of carbonfibers may be tested in the same time at the same costs which leads to ahigher number of pieces in routine piece tests and lower piece costs. Afurther aspect is the fact that the detection of the fiber direction isexecuted based on physical laws and not by calculations using software,which is why the detection of the fiber direction is substantially moresecure. This in particular applies to fabric soaked with plastics wheremethod c) from the introductory part of the description which was usedup to now works relatively restrictedly and inaccurately.

In general, above embodiments may be used in many different fields oftechnology. For example, use in lightweight construction would bepossible where carbon fibers are processed into so-called CFK (carbonfiber reinforced plastics) and quality of the products has to beguaranteed. Examples are aerospace, auto vehicle construction, windpower plants, etc.

Although some aspects have been described in connection with a device,it is obvious that those aspects also represent a description of thecorresponding method, so that a block or a member of a device may alsobe regarded as a corresponding method step or as a feature of a methodstep. Analog to that, aspects which were described in connection with oras a method step also represent a description of a corresponding blockor detail or feature of a corresponding device. Some or all of themethod steps may be executed by a hardware apparatus (or using ahardware apparatus), like for example a microprocessor, a programmablecomputer or an electronic circuit. In some embodiments, some or more ofthe most important method steps may be executed by such an apparatus.

Without having noted this above, it may be the case that for example thecomputer 26 in FIG. 1 or another processing means determines athree-dimensional fiber direction or a fiber direction in an areaparameterization of the surface 14 of the object 10 from the acquiredpolarization direction which indicates the polarization directiontwo-dimensionally in a projection along the direction along which thereflected light impinges upon the polarization sensor 24, by allocatinga place in a parameterization of the surface 14 of the object 10 to thedetected polarization direction and determining the fiber direction sothat it is in this point tangential to the surface 14 and lies withinthe plane which is spanned by the direction of the reflected light andthe determined polarization direction. Of course, one may also see tothe fact that the surface 14—for example at least at the currentlysampled location—is aligned basically perpendicular to the direction ofthe reflected light and the determined polarization direction. Ofcourse, one may also see to the fact that the surface 14—for example atleast at the currently sampled location—is basically alignedperpendicular to the direction of the reflected light.

Hitherto, above embodiments concentrated on the measuring of fiberdirections and utilizing the thus gained information for purposes ofhandling the alignment of the object with respect to other objects. Itis, however, additionally or alternatively possible to use theinformation for other purposes, like e.g. for purposes of qualitycontrol. The polarizing effect of carbon fibers onto reflected light maybe used to test the direction of the carbon fibers during manufacturingcarbon fiber reinforced members and compare the same to given values.This test may be executed but only with intermediate products, like e.g.the individual carbon fiber layers, but also with respect to completemembers. It may in particular be tested whether the angles of the carbonfibers in the member or object have a mandatory value at each positionof the member or whether the mutual alignment of the fibers in a fabriccomprises a mandatory angle value at each provision.

Thus, in FIG. 1, the computer 26 may also function as an analysis means,like e.g. by a corresponding software executed thereon, and the device20 may represent a quality measurement device. The analysis means maytest whether the determined fiber direction fulfills a default conditionin order to, in case of yes, classify the object 10 as being of asufficient quality, and in case of no, classify the object 10 as notbeing of a sufficient quality. Depending on the result, the analysismeans may cause a manipulator to transport the object 10 to a position Afor rejected objects or to a position B, like e.g. an assembly position.

Testing whether the predetermined condition is fulfilled is, forexample, provided by comparing the fiber direction at a position of thesurface 14 of the object to a neighboring position, like e.g. testingwhether the angle between the two directions lies in a predeterminedangle range. Evaluation may also be executed statistically: a histogramof fiber directions at sampled positions of the surface of the object isgenerated and tested statistically. For example, two modes aredetermined and it is tested, whether the angle distance between the twomodes lies in a predetermined range.

Testing whether the predetermined condition is fulfilled may, however,additionally or alternatively consider a characteristic surfacedirection of the object 10, like e.g. an edge, a main curvature or aperimeter of the surface 14. It may then be tested whether the fiberdirection lies in a predetermined angle range relative to thecharacteristic surface direction. The characteristic surface directionmay be detected automatically by the analysis means by patternrecognition or detection. The automatic detection may, in particular, beexecuted using a polarization-independent recording of the object 10. Incase of using a camera as part of the polarization sensor 24 this iseasily possible.

Finally, it is noted with respect to the above embodiments that it mayalso be the case that the light source is not part of the device or thesystem, but possibly part of the environment. Expressed in other words,the ambient light itself may be used. As described above, the assessmentor evaluation of the polarizing effect may still be restricted to awavelength range, like e.g. the above indicated advantageous wavelengthrange in which the light reflected by the object is not only divided inthe polarization sensor with respect to its polarization, but is alsofiltered spectrally. The passband of the spectral filter may inparticular be in a range between 400 and 1000 nm and have a half widthof smaller or equal 100 nm.

Depending on the determined implementation requirements, embodiments ofthe invention may be implemented in hardware or in software. This inparticular applies to the above-mentioned processing means, controllers,analysis means, etc. The implementation may be executed using a digitalstorage medium, for example a floppy disc, a DVD, a Blue-ray disc, a CD,an ROM, a PROM, an EPROM, an EEPROM or a flash memory, a hard disc oranother magnetic or optical memory on which electronically readablecontrol signals are stored which may cooperate or cooperate with aprogrammable computer system such that the respective method isexecuted. Thus, the digital storage medium may be computer-readable.

Some embodiments according to the invention thus include a data carriercomprising electronically readable control signals which are able tocooperate with a programmable computer system such that one of themethods described herein is executed.

In general, embodiments of the present invention may be implemented as acomputer program product having a program code, wherein the program isoperative to execute one of the methods when the computer programproduct is executed on a computer.

The program code may, for example, also be stored on a machine-readablecarrier.

Other embodiments include the computer program for executing one of themethods described herein, wherein the computer program is stored on amachine-readable carrier.

In other words, one embodiment of the inventive method is thus acomputer program comprising a program code for executing one of themethods described herein, when the computer program is executed on acomputer.

A further embodiment of the inventive method is thus a data carrier (ora digital storage medium or a computer readable medium), on which thecomputer program for executing one of the methods described herein isrecorded.

A further embodiment of the inventive method is thus a data stream or asequence of signals which represent the computer program for executingone of the methods described herein. The data stream or the sequence ofsignals may for example be configured so as to be transferred via a datacommunication connection, for example via the internet.

A further embodiment includes a processing means, for example a computeror a programmable logics device which is configured or adapted toexecute one of the methods described herein.

A further embodiment includes a computer on which the computer programfor executing one of the methods described herein is installed.

A further embodiment according to the invention includes a device or asystem which is configured to transfer a computer program for executingat least one of the methods described herein to a receiver. Transmissionmay be executed electronically or optically. The receiver may forexample be a computer, a mobile device, a memory device or a similardevice. The device or the system may for example include a file serverfor transferring the computer program to the receiver.

In some embodiments, a programmable logics device (for example a fieldprogrammable gate array, an FPGA) may be used to execute some or allfunctionalities of the methods described herein. In some embodiments, afield programmable gate array may cooperate with a microprocessor inorder to execute one of the methods described herein. In general, themethods are in some embodiments executed by any hardware device. Thesame may be a universally usable hardware, like a computer processor(CPU) or hardware which is specific for the method, like for example anASIC.

The above described embodiments merely represent an illustration of theprinciples of the present invention. It is obvious that modificationsand variations of the arrangements and details described herein areobvious to other persons skilled in the art. It is thus desired for theinvention to only be restricted by the scope of the following patentclaims and not by specific details presented herein with respect to thedescription and the specification of the embodiments.

Although this invention was described with respect to severalembodiments, there are changes, permutations and equivalents which arewithin the scope of this invention. It is further to be noted that thereare many alternative types for implementing the methods and combinationsof the present invention. It is thus desired for the following appendedclaims to be interpreted as including all such changes, permutations andequivalents which are part of the true nature and scope of the presentinvention.

1. A device for measuring a fiber direction of a carbon fiber materialof a test object, comprising: a polarization sensor for detecting apolarization direction of light reflected by the test object, thepolarization direction indicating the fiber direction.
 2. The deviceaccording to claim 1, further comprising a light source for illuminatingthe test object.
 3. The device according to claim 2, wherein the lightsource is implemented to illuminate the test object with light lyingwithin a range between 400 and 1000 nm.
 4. The device according to claim1, wherein the polarization sensor comprises a polarization-sensitivecamera for recording the test object in order to acquire a spatiallyresolved detection of the polarization direction and thus a spatiallyresolved sampling of the fiber direction.
 5. The device according toclaim 4, wherein the polarization-sensitive camera comprises a pixelarray and an objective for imaging the test object onto the pixel array,wherein pixels of the pixel array are grouped into super-pixels so thateach super-pixel comprises pixels of the pixel array which are sensitivewith respect to different polarization directions.
 6. The deviceaccording to claim 5, wherein each pixel comprises a photo-sensitivearea and a polarization filter structure upstream from thephoto-sensitive area, wherein the filter structure comprises a grid orstructure elements with dimensions in the sub-wavelength range.
 7. Thedevice according to claim 4, wherein the device is implemented to outputthe spatially resolved sampling of the fiber direction in a colorencoded way.
 8. The device according to claim 1, further comprising aspectral filter for spectrally filtering the light reflected by theobject whose polarization direction is detected by the polarizationsensor.
 9. The device according to claim 8, wherein a passband of thespectral filter lies within a range between 400 and 1000 nm.
 10. Thedevice according to claim 1, wherein the device comprises a controllerwhich is implemented to control a manipulator for holding and changingthe position of the object depending on position information withrespect to a position of the object relative to the polarization sensorand on the fiber direction of the object.
 11. The device according toclaim 1, wherein the device comprises a controller which is implementedto control a manipulator for positioning the object and another objectnext to each other depending on position information on a position ofthe object relative to the polarization sensor and the fiber directionof the object, so that in an adjoined state the fiber directioncomprises a predetermined orientation with respect to the other.
 12. Thedevice according to claim 1, wherein the device comprises a controllerwhich determines an orientation of the fiber direction relative to adesign of the object depending on position information on a position ofthe Object relative to the polarization sensor and on the fiberdirection of the object.
 13. The device according to claim 1, whereinthe device comprises a processor implemented to determine athree-dimensional fiber direction or a fiber direction in an areaparameterization of a surface of the object from the detectedpolarization direction so that the determined fiber direction istangential to the surface and lies in a plane spanned by a direction ofthe reflected light and the detected polarization direction.
 14. Thedevice according to claim I, wherein the device comprises an analyzerwhich is implemented to test whether the fiber direction fulfills apredetermined condition to test a quality of the object.
 15. A systemfor manufacturing an object in a carbon fiber composite construction,comprising: a device for measuring a fiber direction of a carbon fiberlayer of a carbon fiber material of a test object, comprising: apolarization sensor for detecting a polarization direction of lightreflected by the test object, the polarization direction indicating thefiber direction; and a manipulator for placing the carbon fiber layerson top of each other adjusting the fiber directions of the carbon fiberlayers according to the measurement by the device.
 16. The systemaccording to claim 15, further comprising provider for providing thecarbon fiber layers with plastics, so that the carbon fiber layers areembedded into plastics after a curing of said plastics.
 17. A method formeasuring a fiber direction of a carbon fiber material of a test object,comprising: illuminating the test object; and detecting a polarizationdirection of light reflected by the test object, the polarizationdirection indicating the fiber direction.
 18. A computer programcomprising a program code for executing the method for measuring a fiberdirection of a carbon fiber material of a test object, comprising:illuminating the test object; and detecting a polarization direction oflight reflected by the test object, the polarization directionindicating the fiber direction, when the program is executed on acomputer.